While the invention is regarded as having application to the knitting of goods other than compressive stockings, the provision of an improved knitting machine and method for knitting compressive stockings as well as an improved compressive stocking construction are used as illustrative examples of how the invention is applied. The background art is thus explained with these examples in mind.
It has long been known that elastic support stockings provide effective treatment for various chronic venous insufficiences. In some instances, the patient can be fitted with immediately-available, ready-made hosiery. However, because of the wide range of leg lengths and sizes, some patients require elastic support stockings made to a specific prescription for the patient's individual requirements.
One conventional method for making a compressive stocking according to a specific patient prescription involves measuring the patient's limb to be fitted at various locations along the length of the limb, cutting a piece of flat elastic fabric to conform to the patient's specific limb dimensions and then completing the stocking by joining the edges into a longitudinal seam. U.S. Pat. No. 2,816,361 describes such a method for cutting an elastic fabric blank corresponding to the dimensions of a specific patient recorded on a special tape device and then seaming the blank at the edges to provide a compressive stocking corresponding to a particular patient's specific needs. U.S. Pat. No. 2,807,946 describes a method of making a shaped compressive stocking on a circular knitting machine by increasing and decreasing the tension applied to the elastic or so-called "rubber" feed during knitting. While the specific type of machine control contemplated in U.S. Pat. No. 2,807,946 is not described, it would be expected that such rubber feed tension control would be under mechanical control on the machine.
In view of the fact that the present invention is directed in part to a program-controlled knitting operation it is also recognized that circular knitting machines have previously been operated under program control as distinct from use of a conventional pattern drum, or the like. For example, U.S. Pat. No. 3,069,881 teaches a punched card system with means to read the cards so as to control the knitting machine elements during the knitting sequence.
U.S. Pat. No. 3,232,079, in another example of a program-controlled circular knitting machine discloses a circular knitting machine in which program responsive electrical control means control various knitting elements, including raising and lowering the cylinder, to control the form of the circular knit fabric produced on the machine. However, this patent makes no suggestion or teaching for storing body, e.g., leg dimensions, or the like, for a specific patient and using this information in conjunction with known compressive characteristics obtainable from various machine settings also stored as a means for knitting a compressive stocking under program control to a specific prescription.
U.S. Pat. Nos. 3,670,527; 3,861,178; 3,866,442 and 4,018,064 further exemplify the state of the art with regard to program-controlled knitting machines.
Recognition is also given to the fact that storing of a specific size in memory and controlling a knitting machine to knit such size has been known. However, such machines do not provide for accommodation to a specific patient's needs nor do such machines progressively control both size and pressure.
With the above background art in mind, it becomes apparent that the art has not provided a satisfactory method for making compressive stockings according to prescription so as to provide a graduated pressure profile suited to the particular patient's limb dimensions and medical requirements. More specifically, none of the prior art methods or prior art circular knitting machines are adapted to produce a compressive stocking with a smooth, graduated transition in pressure from the ankle, through each leg segment point up to the gluteal furrow and with pressures determined so as to satisfy a physician-specified pressure profile based on the patient's needs. A critical analysis of so-called customized or prescription-made compressive support stockings according to the prior art reveals undesirable transitions in pressure. Also, the pressures do not correspond to the most desirable pressure profile and the profile is generally not precisely reproducible when a need for replacement occurs.